When cfq I/O scheduler is selected, get_request() in __make_request() calls
__cfq_get_queue(). __cfq_get_queue() finds an existing queue (struct
cfq_queue) of the current process for the device and returns it. If it's not
found, __cfq_get_queue() creates and returns a new one if __cfq_get_queue() is
called with __GFP_WAIT flag, or __cfq_get_queue() returns NULL (this means that
get_request() fails) if no __GFP_WAIT flag.
On the other hand, in __make_request(), get_request() is called without
__GFP_WAIT flag at the first time. Thus, the get_request() fails when there is
no existing queue, typically when it's called for the first I/O request of the
process to the device.
Though it will be followed by get_request_wait() for general case,
__make_request() will just end the I/O with an error (EWOULDBLOCK) when the
request was for read-ahead.
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
diff --git a/drivers/block/cfq-iosched.c b/drivers/block/cfq-iosched.c
index 0ef7a00..2210bac 100644
--- a/drivers/block/cfq-iosched.c
+++ b/drivers/block/cfq-iosched.c
@@ -1202,13 +1202,16 @@
if (new_cfqq) {
cfqq = new_cfqq;
new_cfqq = NULL;
- } else if (gfp_mask & __GFP_WAIT) {
+ } else {
spin_unlock_irq(cfqd->queue->queue_lock);
new_cfqq = kmem_cache_alloc(cfq_pool, gfp_mask);
spin_lock_irq(cfqd->queue->queue_lock);
+
+ if (!new_cfqq && !(gfp_mask & __GFP_WAIT))
+ goto out;
+
goto retry;
- } else
- goto out;
+ }
memset(cfqq, 0, sizeof(*cfqq));
